(CNN) -- Gas prices have jumped again nationwide, according to a survey published Sunday.
The average price for a gallon of regular is now $3.76 -- up nearly seven cents from two weeks ago, the Lundberg Survey found.
The increase is substantially smaller than in the previous two weeks, when the price jumped nearly 19 cents a gallon.
"Higher crude oil and higher ethanol prices have worked their way into the pump," said publisher Trilby Lundberg.
But gasoline use generally tapers off with cooler weather, as fewer people take to the roads for trips. So in September, demand will probably fall.
"So if there is no oil or gasoline supply cut, then there's a very good chance that we've seen the end of the pump price hikes," Lundberg said.
It's too soon to tell what impact Tropical Storm Isaac may have, she said.
A deadly explosion at an oil refinery in Venezuela could affect prices as well, Lundberg said. But so far this and other recent events have not led to any shortage of oil, she said.
Prices peaked this year in early April, at a national average of $3.97 -- 21 cents higher than in the latest survey.
At this time a year ago, the average was $3.61 -- 15 cents lower than it is now.
The Lundberg Survey tallies prices at thousands of gas stations nationwide.
The city with the lowest average price in the latest survey was El Paso, Texas, at $3.32. The high was in Chicago, at $4.22.
Here are average prices in some other cities:
• Boston - $3.78
• Philadelphia - $3.78
• Norfolk, Virginia - $3.60
• Atlanta - $3.78
• Denver - $3.44
• Phoenix - $3.50
• Billings, Montana - $3.57
• Portland, Oregon - $3.96
CNN's Josh Levs contributed to this report.